Typically, radio receivers include a reference oscillator. The reference oscillator is used to generate all the frequencies required to demodulate the received signal. If the phase of the intermediate frequency (IF) signal will be directly digitized, then a detector reference signal must be generated having a frequency equal to the IF; otherwise, the digitized phase signal will need to be corrected for the difference in frequencies after the digital detection. For example, assume the radio receiver has a reference oscillator of 16.8 megahertz (MHz) and an IF (f.sub.i) of 456 kilohertz (kHz). Using an N-bit phase digitizer circuit operating at the reference oscillator frequency (f.sub.ref) results in a digital detector reference frequency (f.sub.o) equal to f.sub.ref divided by 2.sup.N. With a 5-bit phase digitizer circuit, the detector reference frequency would be equal to 16.8 MHz divided by 2.sup.5, or 525 kHz. Thus, the digital detector reference frequency (f.sub.o) does not equal the IF (f.sub.i). To directly digitize the phase, the IF and the digital detector reference frequency must be matched. Two solutions are currently available.
First, another reference oscillator could be used to generate a detector reference frequency equal to the IF. In the previous example, the digital phase detector would require a second reference oscillator generating a frequency of 14.592 MHz (14.592/2.sup.5 =456 kHz). Several disadvantages result from the use of the second reference oscillator. First, a non-standard frequency would require a specialized design and additional cost. Second, an additional oscillator increases the cost, size, and power consumption within the radio receiver. Third, having two unique frequencies generated within the radio receiver can potentially cause spurious interference problems. Thus, adding a reference oscillator is an undesirable solution to this problem.
A second solution to the problem involves translating the frequency of the IF signal (f.sub.i) to match the frequency of the detector reference (f.sub.o). This can be implemented by mixing the IF signal with a local oscillator (LO) whose frequency is equal to the difference f.sub.o -f.sub.i. Furthering the preceding example, the IF of 456 kHz would need to be mixed up such that it was equal to 525 kHz. The mixing would required an LO frequency equal to f.sub.o -f.sub.i, or 69 kHz. In addition to the extra hardware required, this solution can also cause spurious interference problems. Hence, analog frequency translation is also an undesirable solution to this problem.
Therefore, a need exists for a small, low cost, frequency translation device which does not require any additional analog hardware or create any potential spurious interference problems.